Field
Embodiments of the present disclosure relate generally to metal production and, in certain embodiments, relates to methods of producing metallic tubular bars having high toughness at low temperature while concurrently possessing sulfide stress corrosion cracking resistance. Certain embodiments relate to seamless steel pipes for risers of all kinds (catenary, hybrid, top tension, work over, drilling, etc.), line pipes and flow lines for use in the oil and gas industry, including pipes that are suitable for bending.
Description of the Related Art
A core component in deep and ultra-deep sea production is the circulation of fluids from the seafloor to the surface system. Risers, the pipes which connect the drilling or production platform to the well, are exposed over considerable length (now exceeding roughly 10,000 feet, or approximately 2 miles) to the straining pressures of multiple ocean currents.
Riser system costs are quite sensitive to water depth. Although in-service conditions and the sensitiveness of environmental loads (i.e. wave and current) are different for the for the different riser types—Top Tension Risers (TTRs) and Steel Catenary Risers (SCRs), Hybrid Risers (HRs), Work over (WORs) and Drilling Risers (DRs)—reducing the raiser weight may provide significant benefits. For example, by reducing the weight of the line, it is anticipated that a decrease in the cost of the pipe and a significant impact on the tensioning system used to support the riser may be achieved. For at least these reasons, high strength steels, with yield stresses of about 70 ksi (485 MPa) and above, may be candidates for development of lighter risers in the offshore sector.
However, steels with specified minimum yield strength (SMYS) exceeding about 70 ksi can suffer sulfide stress corrosion (SSC) induced failures as a result of hydrogen embrittlement under stress. Therefore, it is difficult to meet the NACE requirement for sour service materials (e.g., NACE MR0175/ISO 15156-1 “Petroleum and natural gas industries—Materials for use in H2S-containing Environments in oil and gas production—Part 1: General principles for selection of cracking-resistant materials) and to pass SSC testing (e.g., NACE Standard TM0177 “Laboratory testing of metals for resistance to sulfide stress cracking and stress corrosion cracking in H2S environments”).
While major seamless line pipe manufacturers are able to manufacture high strength materials with minimum yield strength equal or above about 70 ksi, resistance to SSC and hydrogen induced cracking (HIC) (this latter assessed according with NACE Standard TM0284, “Evaluation of pipeline and pressure vessel steels for resistance to hydrogen induced cracking”) of these high grades is often not adequate. Currently, only grades up to X70 are rated for sour service according to ISO 3183.
Moreover, increased strength may lead to more brittle behavior at lower temperatures. In general the materials are qualified at so-called “design temperatures”, which typically lie at about 20° C. below minimum expected service and/or ambient temperature. The lowest ambient temperature on the Norwegian continental shelf is about −20° C. In the Arctic regions, minimum ambient temperatures well below −40° C. are expected. Consequently, minimum design temperatures down to approximately −60° C. are desired.
However, line pipe steels with yield stresses of about 70 ksi and above are today qualified for design temperatures only down to about −40° C. This limitation could limit cost-effective oil and gas exploration in arctic and arctic-like regions. Therefore new high strength steel pipes with improved toughness at temperatures equal or less than about −60° C. are desirable.